1. Field of the Invention
The present invention relates to syringes. More specifically, the present invention relates to syringes that include devices that apply a biasing force to the piston of the syringe and acts to automatically expel material from the syringe.
2. Description of the Prior Art
The prior art record is replete with different types and styles of syringes. Generally, a syringe is a device for dispensing liquid in a controlled manner. Syringes typically contain a barrel and a piston that moves back and forth within the barrel. A cannula communicates with the barrel so that a liquid can be either ejected from, or drawn into, the syringe. If the barrel of a syringe is filled with a liquid and the piston is advanced into the syringe barrel, the liquid will be extruded through the cannula. Conversely, if the syringe barrel is empty and the piston is retracted, a negative pressure will occur within the syringe barrel that will act to draw liquid into the syringe barrel through the cannula.
With a common syringe, a person's hands are used to either advance or retract a piston within a syringe barrel. However, in many applications, it is desired to slowly move the piston of a syringe over a prolonged predetermined period of time. One such application is when a syringe is used to inject an active solution into a tree.
Arborists commonly inject trees with active solutions. The solutions may be antimicrobials, nutritional supplements or herbicides. To inject a tree, the arborist commonly drills a hole into the cambium layer and/or xylem of the tree. A cannula from a syringe is then placed into the drilled hole. The syringe is filled with the active solution. The active solution is slowly ejected from the syringe as the tree absorbs the solution into its sap and distributes the active solution throughout the tree.
It may take a tree hours to absorb all the active solution in a syringe. Obviously, it is not desirable for a person to sit by the syringe for that period of time and apply an extruding bias to the piston of the syringe. For this reason, spring biased syringes have been developed in the prior art. Spring biased syringes contain an integral spring that biases a syringe piston in one direction until all the liquid contained within the syringe barrel is expelled. Such prior art syringes are exemplified by U.S. Pat. No. 5,239,773 to Doolittle, entitled Tree Injection System; U.S. Pat. No. 5,318,539 to O'Neil, entitled Liquid Feeding Apparatus Utilizing Capillary Tubing And Syringe Driver; and U.S. Pat. No. 5,693,021 to Diaz, entitled Catheter Exchange Device.
With all the spring biased syringes cited, the syringes are custom manufactured with the spring being an integral part of the syringe's design. Such spring biasing mechanisms cannot therefore be retroactively added to common syringes. Since the spring bias mechanism of such prior art syringes are integrally designed as part of the syringes, the springs of the syringe automatically become compressed when the syringe is filled. Since the syringes are commonly filled with active ingredients that many be harmful to humans, the syringes have the potential of expelling that harmful material if accidently activated. According, filled prior art syringes are dangerous to transport and handle. A need therefore exists for a system where a spring biasing mechanism can be selectively added to common inexpensive syringes after the syringe is safely applied. The syringe can therefore be safely transported and handled without the contents of the syringe being under pressure. After being used, the spring biasing mechanism can be removed and the syringe can be either refilled or disposed. The spring biasing mechanism can then be used again on the same syringe or on another syringe.